A Search for CO (J=3--2) Emission from the Host Galaxy of GRB980425 with the Atacama Submillimeter Telescope Experiment
著者
和文:
Hatsukade, B.,
Kohno, K.,
Endo, A.,
Tosaki, T.,
Ohta, K.,
Sakamoto, S.,
河合 誠之,
Cortés, J. R.,
Nakanishi, K.,
Okuda, T.,
Muraoka, K.,
Sakai, T.,
Vreeswijk, P. M.,
Ezawa, H.,
Yamaguchi, N.,
Kamegai, K.,
Kawabe, R..
英文:
Hatsukade, B.,
Kohno, K.,
Endo, A.,
Tosaki, T.,
Ohta, K.,
Sakamoto, S.,
Kawai, N.,
Cortés, J. R.,
Nakanishi, K.,
Okuda, T.,
Muraoka, K.,
Sakai, T.,
Vreeswijk, P. M.,
Ezawa, H.,
Yamaguchi, N.,
Kamegai, K.,
Kawabe, R..
We report on a deep search for 12CO (J=3-2) line emission from the host galaxy of GRB980425 with the Atacama Submillimeter Telescope Experiment (ASTE). We observed five points of the galaxy, covering the entire region. After combining all of the spectra, we obtained a global spectrum with a rms noise level of 3.3 mK in the Tmb scale at a velocity resolution of 10 km s-1. No significant emission was detected, though we found a marginal emission feature in the velocity range corresponding to the redshift of the galaxy. We derived 3 σ upper limits on the global properties: the velocity-integrated CO (3-2) intensity of ICO(3-2) < 0.26 K km s-1, by adopting a velocity width of 67 km s-1; an H2 column density of N(H2) < 3 × 1020 cm-2; a molecular gas mass of M(H2) < 3 × 108 Modot, by assuming a CO line luminosity to H2 molecular gas mass conversion factor of XCO = 5.0 × 1020 cm-2 (K km s-1)-1; and a star-formation rate of SFR < 0.1Modot yr-1, based on the Schmidt law. The SFR is consistent with the previous results of Hα and mid-IR observations, thereby suggesting that there is no significant obscured star formation in the host galaxy of GRB980425. This result implies that there is a variety of GRB hosts with regard to the presence of obscured star formation.
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